What is it? and why would some company still be looking for someone who knows this language?

Today the company is a monster involved in all sorts of stuff. They started out with a statistics package (API and callable services) that was used by social science guys called SAS (Statistical Analysis System) for IBM mainframes. You called their subroutines from assembler language (and maybe Fortran/PL/I/COBOL programs, I can't remember, it was thirty years ago) to do complex statistics stuff. College kids used to use it in their courses.

Later they became famous for a C compiler, also for IBM mainframes because IBM was slow in bringing a good C compiler to the market as virtually all of IBM OS and product code was (and probably still is) written in assembler, plas, and PL/X. Now you can see from that link how much they're involved in.